Heat pipe evaporator with porous valve

ABSTRACT

An evaporator includes an enclosure having a fluid inlet manifold and a vapor outlet manifold. At least one blind passageway is arranged within the enclosure so as to open into a portion of the vapor outlet manifold. The interior surface of the enclosure that defines each passageway is covered with a capillary wick. A porous valve is arranged in fluid communication between the fluid inlet manifold and a blind end of the at least one blind passageway.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 60/499,483, filed Sep. 2, 2003 and U.S. ProvisionalPatent Application No. 60/502,125, filed Sep. 11, 2003.

FIELD OF THE INVENTION

The present invention generally relates to evaporators for use inthermal management systems, and more particularly to evaporatorsutilizing two-phase coolants.

BACKGROUND OF THE INVENTION

It has been suggested that a computer is a thermodynamic engine thatsucks entropy out of data, turns that entropy into heat, and dumps theheat into the environment. The ability of prior art thermal managementtechnology to get that waste heat out of semiconductor circuits and intothe environment, at a reasonable cost, limits the density and clockspeed of electronic systems.

A typical characteristic of heat transfer devices for electronic systemsis that a semiconductor chip often thermally contacts a passive heatspreader plate, which conducts the heat from the chip to the evaporatorof one of several types heat transfer devices, and then on into theatmosphere. As the power to be dissipated by semiconductor devicesincreases with time, a problem arises: over time the thermalconductivity of the available materials becomes too low to conduct theheat from the semiconductor device to the atomosphere with an acceptablylow temperature drop. The thermal power density emerging from thesemiconductor devices will be so high that even copper or silverspreader plates will not be adequate.

Thermal energy can sometimes be transported by an intermediate loop ofrecirculating fluid; heat from the hot object is conducted into a heattransfer fluid, the fluid is pumped by some means to a differentlocation, and there the heat is conducted out of the fluid into theatmosphere. For example, thermosyphons use a change in density of theheat transfer fluid to impel circulation of the fluid, while heat pipesand boiling fluorocarbons use a phase transition in the heat transferfluid to impel circulation of the fluid. While these approaches haveimportant cooling applications, their cost for implementation will haveto be reduced to generally impact semiconductor cooling.

Another technology that has proven beneficial is the heat pipe. A heatpipe includes a sealed envelope that defines an internal chambercontaining a capillary wick and a working fluid capable of having both aliquid phase and a vapor phase within a desired range of operatingtemperatures. When one portion of the chamber is exposed to relativelyhigh temperature it functions as an evaporator section. The workingfluid is vaporized in the evaporator section causing a slight pressureincrease forcing the vapor to a relatively lower temperature section ofthe chamber, defined as a condenser section. The vapor is condensed inthe condenser section and returns through the capillary wick to theevaporator section by capillary pumping action. Because a heat pipeoperates on the principle of phase changes rather than on the principlesof conduction or convection, a heat pipe is theoretically capable oftransferring heat at a much higher rate than conventional heat transfersystems. Consequently, heat pipes have been utilized to cool varioustypes of high heat-producing apparatus, such as electronic equipment(See, e.g., U.S. Pat. Nos. 5,884,693, 5,890,371, and 6,076,595).

Electronic systems must not only be cooled during their working life,but also during initial packaging, and testing prior to use in acommercial product. In many testing applications, the tests must beperformed at elevated temperatures. Automated test systems are commonlyoutfitted with temperature control systems which can control thetemperature of the device or devices under test. For example, andreferring to FIG. 5, a semiconductor device test system A often includesa temperature-controlled semiconductor device support platform B that ismounted on a prober stage C of prober station D. A top surface E of thedevice support platform B supports a semiconductor device F andincorporates conventional vacuum line openings and grooves Gfacilitating secure holding of semiconductor device F in position on topsurface E of device support platform B. A system controller is providedto control the temperature of device support platform B. A coolingsystem I is provided to help regulate the temperature of device supportplatform B. A user interface is provided in the form of a touch-screendisplay J where, for example, a desired temperature for the top ofsupport platform B can be input. Temperature controlled systems fortesting semiconductor devices during burn-in are well known, asdisclosed in the following patents which are hereby incorporated byherein by reference: U.S. Pat. Nos. 4,037,830, 4,213,698, RE31053,4,551,192, 4,609,037, 4,784,213, 5,001,423, 5,084,671, 5,382,311,5,383,971, 5,435,379, 5,458,687, 5,460,684, 5,474,877, 5,478,609,5,534,073, 5,588,827, 5,610,529, 5,663,653, 5,721,090, 5,730,803,5,738,165, 5,762,714, 5,820,723, 5,830,808, 5,885,353, 5,904,776,5,904,779, 5,958,140, 6,032,724, 6,037,793, 6,073,681, 6,245,202,6,313,649, 6,394,797, 6,471,913, 6,583,638, and 6,771,086.

None of the foregoing technologies or devices has proved to be entirelysatisfactory.

SUMMARY OF THE INVENTION

The present invention provides an evaporator including an enclosurehaving a fluid inlet manifold and a vapor outlet manifold. At least oneblind passageway is arranged within the enclosure so as to open into aportion of the vapor outlet manifold. The interior surface of theenclosure that defines each passageway is covered with a capillary wick.A porous valve is arranged in fluid communication between the fluidinlet manifold and a blind end of the at least one blind passageway.

In another embodiment of the invention an evaporator is provided thatincludes an enclosure having a fluid inlet manifold and a vapor outletmanifold arranged in substantially parallel spaced relation within theenclosure. A plurality of blind passageways are provided that each openinto a portion of the vapor outlet manifold. A capillary wick covers theinterior surfaces of the evaporator that define each of the passageways.A plurality of porous valves are arranged in fluid communication betweenthe fluid inlet manifold and a blind end of each one of the plurality ofblind passageways.

A thermal management system is also provided that includes at least oneevaporator comprising an enclosure having a fluid inlet manifold and avapor outlet manifold. At least one blind passageway is defined withinthe enclosure that opens into a portion of the vapor outlet manifold.The interior surfaces of the enclosure that define each passageway arecovered with a capillary wick. A porous valve is arranged in fluidcommunication between the fluid inlet manifold and a blind end of eachblind passageway that is provided in the enclosure. A condenser assemblyis also provided that has an inlet opening arranged in flowcommunication with the vapor outlet manifold of the at least oneevaporator and an outlet opening arranged in fluid communication withthe fluid inlet manifold of the at least one evaporator. A pump isoperatively positioned between the fluid inlet manifold and the outletopening so as to force a coolant liquid into the inlet manifold at apredetermined pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bemore fully disclosed in, or rendered obvious by, the following detaileddescription of the preferred embodiment of the invention, which is to beconsidered together with the accompanying drawings wherein like numbersrefer to like parts and further wherein:

FIG. 1 is a perspective view of an evaporator formed in accordance withthe present invention;

FIG. 2 is a perspective, transverse cross-sectional view of theevaporator shown in FIG. 1;

FIG. 3 is a plan view of the cross-section shown in FIG. 2;

FIG. 4 is a front elevational view of a typical semiconductor deviceburn-in-testing station;

FIG. 5 is an exploded perspective view of a typical semiconductor devicemounted for burn-in-testing, and positioned above an evaporator formedin accordance with the present invention;

FIG. 6 is a schematic, partially cross-sectioned, representation of acooling system utilizing an evaporator formed in accordance with thepresent invention;

FIG. 7 is an enthalpy versus pressure diagram providing an operatingcurve for use in connection with the evaporator of the presentinvention; and

FIG. 8 is an alternative embodiment of an evaporator formed inaccordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

This description of preferred embodiments is intended to be read inconnection with the accompanying drawings, which are to be consideredpart of the entire written description of this invention. The drawingfigures are not necessarily to scale and certain features of theinvention may be shown exaggerated in scale or in somewhat schematicform in the interest of clarity and conciseness. In the description,relative terms such as “horizontal,” “vertical,” “up,” “down,” “top” and“bottom” as well as derivatives thereof (e.g., “horizontally,”“downwardly,” “upwardly,” etc.) should be construed to refer to theorientation as then described or as shown in the drawing figure underdiscussion. These relative terms are for convenience of description andnormally are not intended to require a particular orientation. Termsincluding “inwardly” versus “outwardly,” “longitudinal” versus “lateral”and the like are to be interpreted relative to one another or relativeto an axis of elongation, or an axis or center of rotation, asappropriate. Terms concerning attachments, coupling and the like, suchas “connected” and “interconnected,” refer to a relationship whereinstructures are secured or attached to one another either directly orindirectly through intervening structures, as well as both movable orrigid attachments or relationships, unless expressly describedotherwise. The term “operatively connected” is such an attachment,coupling or connection that allows the pertinent structures to operateas intended by virtue of that relationship. In the claims,means-plus-function clauses are intended to cover the structuresdescribed, suggested, or rendered obvious by the written description ordrawings for performing the recited function, including not onlystructural equivalents but also equivalent structures.

Referring to FIGS. 1–3, an evaporator 2 formed in accordance with thepresent invention includes an inlet manifold 4, an outlet manifold 6, aplurality of blind passageways 11, and a porous valve 13. Evaporator 2is formed in an enclosure that is formed from a highly thermallyconductive material, e.g., copper or its alloys, aluminum or its alloys,or steel. An enclosure for purposes of this description will usuallymean a walled or otherwise inclosed, shut up, or encompassed void (orvoids) that is separated from surrounding structures by a plurality ofsolid dividing structures, e.g., walls. An evaporator enclosure 2 of thetype used in connection with the present invention often comprises asubstantially flat aspect ratio so as to complement a variety of flatheat sources, e.g., a wide variety of semiconductor devices andpackages. Inlet manifold 4 and outlet manifold 6 often comprisesubstantially parallel blind bores that are located in spaced relationto one another within evaporator 2. An inlet opening 14 in a sidesurface (FIGS. 1, 2, and 3) or top surface (FIG. 8) of evaporator 2 isarranged in open flow communication with inlet manifold 4 and acondenser assembly 26, via a coolant conduit 28 (FIGS. 2, 3, and 7) andan outlet opening 16 is arranged in flow communication with outletmanifold 6 and condenser assembly 26, via vapor conduit 29.

Plurality of blind passageways 11 are often arranged in substantiallyparallel relation to one another, with each having an open end 30 thatopens into outlet manifold 6. The portions 31 of evaporator enclosure 2that reside between adjacent passageways 11 serve as “fins” todistribute heat to a larger surface. These structures also provideadditional structural support to strengthen evaporator 2. Eachpassageway 11 is lined or covered with a capillary wick 32 formed on theinterior surfaces of evaporator 2 that define each passageway 11.Capillary wick 32 most often comprises a sintered or brazed metal powderstructure with interstices between the particles of powder. Of course,capillary wick 32 may also other wicking structures, such as, grooves,screen, cables, adjacent layers of screening, and felt. In oneembodiment, capillary wick 32 may comprise sintered copper powder,sintered aluminum-silicon-carbide (AlSiC) or copper-silicon-carbide(CuSiC) having an average thickness of about 0.1 mm to 1.0 mm. A coolantfluid 35 saturates capillary wick 32 during operation of evaporator 2,and may comprise any of the well known two-phase vaporizable liquids,e.g., water, alcohol, freon, etc.

A porous valve 13 is formed within evaporator 2 so as to create theblind end of each passageway 11. Porous valve 13 comprises a plug ofporiferous material, e.g., a powdered metal meshwork, that is permeableto coolant fluid 35, but at a substantially reduced rate as compared toan unobstructed portion of passageway 11. As such, porous valve 13 formsa seeping barrier to liquid coolant fluid 35 and between inlet manifold4 and the capillary wick that lines passageway 11. In one embodiment ofthe invention, porous valve 13 may be formed from a sintered material,e.g., copper, with pores sized in a range from about 25 μm to about 150μm, with pores sized in the range of 50 μm to about 80 μm beingpreferred for most applications using water for coolant fluid 35. Thelength of porous valve 13 may be set according to the flow rate throughthe valve that is needed to prevent drying out of capillary wick 32.Porous valve 13 is positioned within evaporator 2 so that an inletsurface 38 is in flow communication with inlet manifold 4.

Evaporator 2 is normally arranged in intimate thermal engagement with asource of thermal energy, such as an integrated circuit chip or chips F,or an electronic device comprising such chips or other heat generatingstructures known in the art. Multiple evaporators 2 may include externaland/or internal features and structures to aid in the rapid vaporizationof coolant fluid 35. For example, an externally applied thermallyconductive coating may used to enhance heat transfer and spreading fromthe heat source throughout evaporator 2.

In operation, evaporator 2 normally forms a portion of a thermalmanagement system 45 (FIG. 4). In one embodiment, thermal managementsystem 45 also includes a condenser assembly 26, a pump 50, and apressure control valve 52. Condenser assembly 26 comprises a chamberedenclosure 55 having an inlet opening 57 arranged in flow communicationwith one or more evaporators 2, via vapor conduit 29, and an outletopening 60 arranged in flow communication with each evaporator 2 throughpump 50 and pressure valve 52, via coolant conduit 28. Condenserassembly 26 acts as a heat exchanger transferring heat contained invaporous coolant fluid 62 to the ambient surroundings or with a liquidcooled, secondary condenser 68 that is located within chamberedenclosure 55, and chilled by a flowing liquid or gas, e.g., chilledwater or air, from a pumped source (not shown).

Pump 50 is arranged in fluid communication between each evaporator 2 andcondenser assembly 26. Pump 50 provides a continuous flow of liquidcoolant 35 to the inlet manifold 4 of each evaporator 2 from condenserassembly 26. Pressure control valve 52 helps to maintain an optimumpressure level within inlet manifold 4 so as to produce a constant andcontinuous seepage of liquid coolant fluid 35 through porous valves 13.FIG. 8 provides a graphical representation of the preferred relationshipbetween the seepage of liquid coolant fluid 35 through porous valves 13as a function of coolant liquid pressure within inlet manifold 4.

As a result of this construction, each blind passageway 11 withinevaporator 2 acts as a driven-heat pipe with a porous valve 13 locatedat one end to maintain capillary wick 32 continuously saturated withcoolant liquid 35. More particularly, thermal energy is absorbed byevaporator 2 from heat source F, e.g., a semiconductor chip, byevaporation of liquid coolant 35 (within those portions of capillarywick 32 that are adjacent to heat source F) to vaporous coolant 62inside each blind passageway 11. Advantageously, capillary wick 32provides nucleation sites for bubble formation and retains coolantliquid 35 so that nearly pure vaporous coolant exits passageway 11 fromopen end 30. Vaporous coolant 62, with its absorbed heat load, isthermodynamically driven to each open end 30 due to a pressuredifference created between heat source F and the heat sink formed byoutlet manifold 6. As this occurs, fresh liquid coolant 35 seeps intoeach driven-heat pipe under a predetermined pressure head of liquidcoolant provided in inlet manifold 4 by the action of pump 35. Thiscauses liquid coolant 50 into each driven-heat pipe, via porous valve13, so as to further wet and thereby replenish capillary wick 32 and toreplace the now vaporized coolant. The heat load is rejected by vaporouscoolant 62 to condenser assembly 26, with consequent condensation ofvaporous coolant 62 to liquid coolant 35. Then, pump 50 forces condensedliquid coolant 35 to return to inlet manifold 4.

It is to be understood that the present invention is by no means limitedonly to the particular constructions herein disclosed and shown in thedrawings, but also comprises any modifications or equivalents within thescope of the claims.

1. An evaporator comprising: an enclosure having a fluid inlet manifoldand a vapor outlet manifold; at least one blind passageway that opensinto a portion of said vapor outlet manifold and is centrally definedwithin a capillary wick; an internal fin structure disposed adjacentsaid capillary wick; and a porous valve arranged in fluid communicationbetween said fluid inlet manifold and a blind end of said at least oneblind passageway.
 2. An evaporator according to claim 1 wherein saidcapillary wick comprises a porous internal surface coating deposited onthe interior surfaces of said enclosure so as to define said at leastone blind passageway.
 3. An evaporator according to claim 1 wherein saidcapillary wick comprises a sintered powder.
 4. An evaporator accordingto claim 1 wherein said capillary wick receives coolant fluid throughsaid porous valve thereby continuously saturating a portion of saidcapillary wick.
 5. An evaporator according to claim 1 wherein saidcapillary wick comprises a structure selected from the group consistingof grooves, screen, cables, adjacent layers of screening, felt, andsintered powders.
 6. A thermal management system comprising: at leastone evaporator including; an enclosure having a fluid inlet manifold anda vapor outlet manifold; at least one blind passageway that opens into aportion of said vapor outlet manifold and is centrally defined within acapillary wick; and a porous valve arranged in fluid communicationbetween said fluid inlet manifold and a blind end of said at least oneblind passageway; a condenser assembly having an inlet opening arrangedin flow communication with said vapor outlet manifold of said at leastone evaporator and an outlet opening arranged in fluid communicationwith said fluid inlet manifold of said at least one evaporator; and apump operatively positioned between said fluid inlet manifold and saidoutlet opening so as to force a coolant liquid into said inlet manifoldat a predetermined pressure.
 7. A thermal management system according toclaim 6 further including a pressure control valve located in flowcommunication between said pump and said inlet manifold for regulatingsaid predetermined pressure.
 8. A thermal management system according toclaim 6 wherein said capillary wick comprises a porous internal surfacecoating deposited on the interior surfaces of said enclosure so as todefine said at least one blind passageway.
 9. A thermal managementsystem according to claim 6 wherein said capillary wick comprises asintered powder.
 10. A thermal management system according to claim 6wherein said capillary wick receives coolant fluid through said porousvalve thereby continuously saturating a portion of said capillary wick.11. A thermal management system according to claim 6 wherein saidcapillary wick comprises a structure selected from the group consistingof grooves, screen, cables, adjacent layers of screening, felt, andsintered powders.
 12. A Thermal management system according to claim 6comprising an internal fin structure disposed adjacent said capillarywick defining said at least one blind passageway.
 13. A thermalmanagement system according to claim 6 comprising a pressure controlvalve arranged in flow control communication with said pump so as tomaintain a predetermined pressure within said inlet manifold.
 14. Athermal management system according to claim 6 wherein said pump isarranged in fluid communication between said at least one evaporator andsaid condenser so as to provide a continuous flow of said coolant liquidto said at least one evaporator from said condenser.
 15. An evaporatorcomprising: an enclosure having a fluid inlet manifold and a vaporoutlet manifold; at least one blind passageway that opens into a portionof said vapor outlet manifold and is centrally defined within acapillary wick: and a porous valve arranged in fluid communicationbetween said fluid inlet manifold and a blind end of said at least oneblind passageway: wherein said evaporator comprises an internal finstructure disposed between adjacent ones of said plurality of blindpassageways.